building pinhole camera - light-tightness

[kaiyen]

Hi all,
I am thinking of building a pinhole camera, probably out of cardboard this first time around. I'd like to make it 4x5. I got the specs, focal length, pinhole size, etc. However, I'm not quite sure how to get the film holder light-tight to the "body." Any suggestions? I'm not that familiar with 4x5 film holders so I don't know how much built-in light-tight-ness there already is (ie - if I just get it up nice and snug on the "box," will that be sufficient?). Should I put some kind of felt on there or something?

thanks,
allan

 

[Lee L]

Allan,

First, build in some sort of corner or rabbet/rebate for the outside edge of the film holder to fit inside of. You can do this for all but the side where the darkslide is. Then find some adhesive-backed soft black sheet foam or felt at a good craft store. Put this along the rabbet where the face of the film holder presses against the camera back. Apply pressure to keep the film holder against this seal with rubber bands, springs & bars, eccentrically rotating bars, or whatever else works for you.

Lee

 

[kaiyen]

Excellent. that's what I was thinking. thanks for confirming.
allan

 

[Lee L]

I forgot to mention; you will probably also need to cut a slot or some sort of relief to catch the ridge on the holder face along the darkslide side. This serves two functions. It creates a baffle where you don't have a light baffling corner around the side of the holder where the slide operates, and it catches the holder so that it doesn't slide out of the camera when you pull the darkslide.

Good luck. Pinholes are a lot of fun.

Lee

 

[ElrodCod]

kaiyen,
You may find this link helpful.

Gary

 

[mmmichel]

Allan,

Black foamcore would work much better than cardboard and at not much more cost. you can find some plans at http://www.stanford.edu/~cpatton/foamcore.html (I built this and it worked very well, without any light leaks). Lee is correct that you will have to 1) cut a slot for the ridge on the filmholder and 2) secure some black felt or something like it to the mounting face. For the second task, I used black flocking paper from Edmund Scientific that I happened to have lying around. It's really great stuff, and pretty cheap, I think any tinkering photographer should have some of it. As far as the rabbet is concerned, it could help hold the filmholder in place, but is not absolutely necessary. When I built my first foamcore camera, I did not build a rabbet and I experienced no light leaks.

PS. I know you said that you had already worked out the focal length, etc., but I would like to recommend that you go really wide ~50mm. At this focal length, the resolution is incredible and the falloff is still quite acceptable.

-Melchi